Centralized traffic controlling system for railroads



Aug. 9,1938. N. D. PRESTON 2,126,209

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Original Filed Nov.26, 1952 5 Sheets-Sheet 1 a m C a j .2 o- I111: E a can i 'l Eli Fla. 1.

ConTrol 5 Sheets-Sheet 2 N. D. PRESTON Original Filed Nov; 26, 1932CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Aug. 9, 19: 8.

Aug. 9, 1938. N. o. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FORRAILROADS Original Filed Nov; 26, 1932 5 Sheets-Sheet 3 A 2 R L I A R RO F M E T S Y S G N I L L O R T N O C C I F A R T D E Z I L A R T N E GAug. 9, 1938.

N. D. PRESTO N Original Filed Nov. 26, 1932 5 Sheets-Sheet 4 mONPatented Aug. 9, l 1938 PATENT OFFICE 2,126,209 CENTRALIZED TRAFFICCONTROLLING SYSTEM FOR RAILROADS I Neil D. Preston, Rochester, N. Y.,assignor to General Railway Signal Company,

' N. Y. Application 18 Claims.

This invention relates to centralized trafiic controlling systems foruse in dispatchingqtrains on railway systems and more particularly tothe communication part of such systems; and an improvement over theinvention disclosed in my earlier filed applications Ser. No. 589,186filed January 27, 1932, and Ser. No. 596,516 filed March 3, 1932, and noclaim is made herein to any invention disclosed in either of saidearlier filed applications.

In railroad trafiic controlling systems the trafiic iscontrolled from acentral control office and also the location of trains and the,condition of the trafilc controlling devices at remote 1ocations areindicated to the attendant at the con- 'trol office. This invention isparticularly useful in such a system which is called upon to carry out,

a large number ofcontrol and indication func-,

tions during a very short time. A single dispatcher can handle thetraffic over a large section of track, so it is apparent that thecontrols and indications should be capable of transmission at such ahigh rate of speed that the accumulation of stored controls andindications. is avoided.

Such a traffic controlling system I is supplemented by the well knownautomatic block .sig nalsystem and other local means ordinarily providedto guard against unsafe train movements, improper operation of trackswitches or the like. The switches and signals are distributed throughout the territory but those located relatively near or adjacent eachother together with the apparatus provided to govern these switches andsignals, are conveniently referred to as. comprising a field station.The communication system is provided to interconnect the control officewith the several field stations and is so organized that completesupervision is obtainedby the operator of the various switch and signaldevices at'the remote stations.

In accordance with the present invention, the

' together. at the last field station of the series in order to providea return circuit for the S line. In accordance with the presentinvention, it is proposed touse the three line wires for transmitting toand from the field stations for selecting and registering field stationsand for actuating con- 55; trolling devices at the field stations andindica- Rochester,

November 26, 1932, Serial No. 644,481

Renewed March 6, 1936 tiondevices at the control office. Combinations ofimpulses of distinctive character are applied to the S line, using the Aand Btlines inmultiple for the return circuit, to select a desired fieldstation, after which a relay or control device for 5 each switch orsignal at the selected station may be actuated or conditioned, by meansof these characteristic impulses-for controlling the respective devicesand therebygoverning the trafiic at the selected station. Such selectionand con- 1n trol is referred to as transmission of controls.

The communication system is also used totransmit to the control officeindications of the positions of the switches and signals and forindicating the presence or absence of trains in particular tracksections, as well as any other indications which may be useful indirecting and supervising train movements. These indications areprecededby the registration in the control office of the particularfield station that is transmitting. This function is automaticallyeffected when a new indication is ready to be transmitted to the controloffice and is conveniently referred to as transmission of indications.

The system is of the coded duplex type and is operated through cycles,during each of which transmission of controls and transmission ofindications can occur separately or simultaneously to and from the samestation or to and from different stations.

When controls are transmitted, a station selecting code is first appliedto the line for selecting the particular station desired, after whichthe controls are transmitted to the selected station by means of codeimpulses. When indications are transmitted, the field stationtransmitting such indications first sends a station registering code forregistering that station in the control ofiice; Thereafter, theparticular indications are transmitted tothe control ofiice by means ofan additional code and are displayed on indicator devices, such as lampsor the like associated with the station sending.

For the transmission of controls, a predetermined number of impulses ofselected polarities is placed on the line circuit for operating theapparatus at the control office and at the field sta tions through acycle of operations, irrespective of the character of the impulses,While the distinctive character of such impulses determines theparticular station to be selected and the controls to be transmitted tothe selected station.

For the transmission of indications, means are provided to condition theA and B lines during a portion ofthe energized periods of the S line forcreating two code characters, either one of which may be selected forconditioning an indication receiving device in the control ofl'ice.During another portion of the energized periods of the S line, the A andB line wires are again conditioned to provide a choice of three codecharacters, any one of whichmay be selected for conditioning anindication receiving device in the office.

gized periods of the S line circuit. The energized periods of the S linecircuit will be referred to as the on periods, while the deenergizedperiods of this line circuit will be referred to as the off periods.

One feature of the present invention relates to the manner in whichindications are preconditioned during the off periods for obtaining achoice of two code characters and the manner in which indications areconditioned during the onperiods for obtaining an additional choice ofthree code characters, with the chosen indications executed during aportion of the on period and a portion of the next succeeding offperiod. For example, insystems of this type, one energizationof thestepping line or on period and one deenergi zation or ofi period has.usually been designated as comprising a single step, with the fieldstation circuits so arranged that indications are transmitted bydistinctively changing or varying the conditioning of the line circuitonce for each step. In the present embodiment, with the S line energizedat the start of an on period, the A or 13 line may be energizedresulting in two distinctive conditions. With the S- line energizedlater during the same on period, the return circuit may be by way ofthe'A line alone, the B line alone or the A and B lines in multiple,

- thus giving three more distinctive conditions resulting in fivedistinctive conditions or code combinations for each step for thetransmission of indications. 7

Obviously, the provision of five distinctive code characters for eachstep results in obtaining twenty-five distinctive codes where eachcomplete code comprises two steps. Similarly, one

hundred and twenty-five distinctive complete codes may be obtained whereeach complete code comprises three steps. In other words, the number ofcode combinations obtained is equal to five raised to the power of thenumber of steps. Therefore, one purpose of the present invention is toprovide a code type selector system which builds up rapidly as thenumber of steps in creases and to accomplish this over a minimum numberof line Wires.

Other objects and advantages of the present invention will behereinafterset forth in the specification and claims and shown in the drawings, thecharacteristic features will be explained more in detail in thefollowing description of one embodiment of the invention, while vari-'which illustrate in a diagrammatic manner the apparatus and circuitsemployed. Those parts having similar features and functions aredesignated in the different figures-by like letter reference characters,generally made distinctive either'by the use of distinctiveexponents-repre- Therefore, a choice of five code char. acters for eachstep is obtained during the enercircuits employed at the control oflice;

Fig. 4 illustrates the apparatus and circuits employed at one of thefieldstations;

Fig. illustrates an operation chart which will be conveniently referredto during the following description for obtaining a concentrated pictureof the sequence of operations of the system during control andindication cycles.

In tracing the detailed circuits, Fig. 4 is placed "tothe right of Fig.2 and Fig. 3 is placed below Fig. 2.

General description The three Wire line circuit which connects thecontrol ofiice with the field stations, extends from the right handportion of Fig. 2 to the left hand portion of Fig. 4, the S line beingin the upper part of these drawings with the A and B lines located nearthe center. The dotted rectangle in the upper right hand portion of Fig.4 indicates that the S line extends through other field stations andincludes other line relays such as F and that the A and B lines extendthrough other field stations and include back contacts of the respectiveimpulsing relays located at these other field stations, such as PLA andPLB This is also clearly indicated in Fig. 1.

It will be understood that these additional stations have apparatus andcircuit arrangements practically the same as that shown in Fig. 2. Aswill be more specifically pointed out in the following description, thepoints of difference in the circuit connections at different fieldstations are the distinctive connections of the code jumpers forconditioning the circuits, so that. a particular field station will befully responsive only to the: particular code assigned to. that station.

For the purpose of simplifying the drawings and facilitating theexplanation, various parts and circuits have been diagrammatically shownand certain. conventional illustrations have been employed. The drawingshave been. made more with the. purpose of making it easy to understandthe principles and mode of operation, than with the idea of illustratingthe specific construction and arrangement of parts and circuits thatwould be. employed in practice. Thus, the various relays and theircontacts are illustrated in a. conventional manner, the use of symbolsbeing employed. to indicate the connections to the terminals ofbatteries, or other sources of current,. instead of showing all of thewire. connections to these terminals.

The symbols. and indicate the positive and negative terminals,respectively, of suitable batteries or other sources of current and thecircuits with which these symbols are used always have current flowingin. the same direction. The symbols (3+) and (B) are employed toindicate the positive and negative terminals, respectively, of asuitable battery, or other source of current, having an intermediate tap(CN) and the circuits with which these symbols. are used may havecurrent flowing in one direction or the other, depending upon whetherthe terminal (B:-|-) or (B)' is used in combination with theintermediate tap (CN).

No attempt has been made to. show all of the apparatus employed, such asthe total'number of manual controls at the control office, the. totalamount of the equipment or its exact arrangement at the field stations,since this apparatus, and equipment may vary to suit local conditions.The character of that apparatus illustrated in the typical controlofiice andthe typical field station will now be, considered. r H

. Control ofiice equipment-As typical of, .the equipment located in thecontrol ofiice-illustrated in Fig. 2, a control machine having axgroupof control levers for each field station is provided. A miniature trackswitch, indicated by reference character ts, corresponds to a particulartrack switch in the v-field and is considered to be representative ofthe actual track layout in the field. Various indicating lamps, orequivalent devices, together with apparatus and circuits to accomplishthe desired operation of the system are likewise provided. The portionof the control ofiice apparatus illustrated in Fig. 2 shows moreparticularly that part of the control machine which is typical of theapparatus associated with a single field station having a track switch,a crossover orthe like, together with the common transmitting apparatusemployed for controlling the circuit operation for all such stations.

7 This equipment for one track switch comprises a switch machine leverSML, a self-restoring starting button SB, the miniature track switch isand the indication lamps RI, NI, UI, OS'and M. Similarly, one or moresignal control levers (not shown) would be associated with the singlefield station, but in order to simplify the drawings and description,these devices have been omitted. It is obvious that the selection of thefield station illustrated in Fig. l, by means of starting button SE ofFig. 2 and thereafter the control of a track switch TS by means of .alever SML may be considered as typical of the selection ofother fieldstations and the control of other traffic controlling devices. 7 i g lTheactuation of the lever SML to one extreme position or the other,followed by the actuation of the starting button SB, results in thenormal or reverse operation of the track switch corresponding to leverSML at that field station which is associated with starting button SB.The momentary actuation of the starting button SB is preferably storedby a storing relay (not shown), which in turn picksup the correspondingcode determiningrelay CD of the associated station. The starting buttonSB is shown connected to the code determining relay CD by means of adotted line in order to simplify the present disclosure.

The storing relays for each starting button and their corresponding codedetermining relays CD are so interconnected that only one relay CD forone particular station may be picked up during one cycle of operations,irrespective of the number of storing relays which are simultaneouslyenergized or energized in rapid succession. This interlocking circuitconnection is so, arranged that if several storing relays are up at thesame time, their corresponding CD relays will be picked up one at a timeduring successive operating cycles, in an order predetermined by theirrelative locations in the bank of relays, all of'which has beencompletely disclosed in the prior ap plication of N. D'..Preston et al.,Ser. No. 455,304, filed May 24, 1 930, corresponding to AustralianPatent No. 1501 of 193 1.

The control ofiizce includes a line relay F, and a i ii f di Iglay wil OWhichaw. nor:

mally down or deenergized during the normal period of rest of the systemand also during the period of blank between, successive operatingcycles.

Slow acting line repeating relays SA and SAP are picked up at thebeginning of each cycle and dropped during the change to normal periodat the end of each cycle. The releasing or dropaway time of relay SA issufiiciently long so that its contacts remain in their actuatedpositions during all.off periods between successive impulses of a cycle,except the last off period which is comparatively long for the purposeof returning the system to the normal period of rest or period of blank.

Associated with the line relay F and its repeating relays is a bank ofstepping relays, including stepping relays IV, 2V and 3V together with ahalf step or steering relay VP, which are provided to mark ofi thesuccessive steps of each cycle. Steering relay VP serves the purpose ofsteering the impulses from relay FP to the proper stepping relay and forsteering the executing circuits to the proper selecting contacts of thestepping relays, all at'the proper time. An impulsing relay E isjointlycontrolled by the stepping relays and the steering relay. Thepick-up and drop-away operations of relay E are repeated by relay EPwhich governs the opening and closing of the S line conductor.

Relay in addition to controlling the line pulsing relay EP, jointlycontrols, with relay FP, the stick circuit of relay MX. Relay E'- alsocontrols the stick circuit of relays MAP and MBP, all of which will bespecifically pointed out in the detailed description. Relay E alsocontrols the circuits over which the indications are executed.

Relay MA is controlled over the A line conductor, relay MB is controlledover the 3 line conductor and their repeating relays MAP and MCBPprovide a choice of five indication code combinations during the onperiod of each step. Relay MX is jointly controlled by relays MAP andMBP to record the choice of two indication code combinations during thefirstpart of the on period with the station code and the controls to betransmitted for that particular cycle.

A starting relay STR. is picked up to initiate a cycle of operationsboth when controls are to be transmitted, due to the manual initiationof the cycle in the control office, and when indications are to betransmitted, due to the automatic initiation of a cycle by a fieldstation. Field start relay FC is picked up when the cycle of opera tionsis initiated by a field station and office start relay 0 is picked upwhen a cycle of operations is initiated by the control oifice.

For the purpose of illustrating station registration, a typical pilotrelay arrangement is shown in Fig. 3. Pilot relays lPT, ZPT and 3PT areconnected to the indication buses so that they may be positioned on thefirst step of the cycle when indications are transmitted. Relay IPT isconnected to No. 1 off bus so that this relay ispositioned to the rightor left as predetermined during the first ofi period. Relay 2PT isconnectedtocNohlAton bus and it. is positioned to the right or left aspredetermined by the condition of the A line conductor during the firston period. Relay 3PT is connected to No. IE on bus and is positioned tothe right or left as predetermined by the condition of the B lineconductor during the first on period. Similarly, additional pilot relays(not shown) may be provided for additional steps up to the point where asufficient number of codes for station registration are obtained.

A station relay ST is provided 'for registering,

in the control ofiice, the station transmitting indications. Relay ST ismerely typical of a number of such relays which would ordinarily beprovided to register individual stations, other relays similar to relayST being connected to the conductors leading to bracket STN. Theconductor indicated phantom, leading to bracket STN, is not used in thisembodiment for connection to a station relay similar to ST. This isbecause when controls alone are being transmitted, the system inherentlytransmits back to the control ofiice a code combination which is notsent by a field station.

A choice of five code characters for each step results in selectivelypositioning the three pilot relays as illustrated in Fig. 3 and althoughsix combinations are obtained, as indicated by the six conductorsconnected to contacts of relay 3PT, only five of these combinations areused since the sixth is associated with the phantom code.

The control machine also includes suitable indication storing relays 1R1R IR and IR for storing the various indications transmitted from thefield stations, after a field station has been registered in the controloflice by the selection of a relay similar to ST. The indication storingrelay IE is controlled in accordance with the occupied or unoccupiedcondition of the detector track section, associated with the outlyingtrack switch illustrated in Fig. 4, as repeated by a track relay T sothat an indicating lamp OS is controlled by the passage of a train.

Indication storing relays IR and IR store the indications of whether theassociated track switch is locked normal, locked reverse, or unlocked inmid-stroke as repeated by the switch repeating relay WP at the station,so that indicator lamps NI, RI, and UI'are displayed to indicate thenormal locked, reverse locked, and the unlocked positions respectivelyof the track switch. Indication storing relay 1R stores any otherrequired condition of a device at the field station such as relay M andcontrols indicating lamp M of Fig. 2 todisplay the condition of thedevice which causes relay M to be up or down.

The fundamentalcoding arrangement for indications disclosed in thepresent invention is. ofparticular advantage, since the preselection oftwo indications during each on period may be used to indicate the twoconditions of a track circuit, that is, occupied or unoccupied.Similarly, there are three conditions of a switch to be indicated,namely, locked normal, locked reverse, or unlocked in mid stroke so thatthe selection of three additional indications during each on period maybe advantageously used for registering these switch conditions. a

Field station equipment.-The field station illustrated in Fig. 4includes, besides the apparatus above mentioned, a quick acting linerelay F and a quick acting line repeating relay FP which repeat the.energizations and deener gizationsof the S line circuit. Relay FPrepeats the impulses in' the S line circuit irrespective of theirpolarities, while relay F is conditioned to the right by a positiveimpulse and to the left by a negative impulse.

A slow acting relay SA of the neutral type repeats the energizedcondition of the FP relay. Relay SA defines the bounds of each cycle ofoperations, being energized at the beginning of each'cycl'e andremaining energized or actuated until the change to normal period at theend of the cycle.

The field station likewise includes a bank of stepping relays IV 2V and3V together with the associated steering or half step relay VP operatingin a similar manner and in synchronism with the stepping relay bank inthe control ofiice. Steering relay VP steers the impulses from relay FPto'the proper stepping relay and it also steers the line impulsingrelays PLA and PLB to the proper indication buses, all at the propertime.

Line impulsing relays FLA and lPLB are provided to open the A and Blines respectively, to provide code combinations during the transmissionof indications, these two relays being conditioned in accordance withthe condition of the indication buses shown in the lower right handportion of Fig. 4. Relay VPC controls the steering relay VP in such away that relay VP can not shift until the line impulsing relays PLA andPLB are in their normal or deenergized positions.

A change repeating relay CHP is provided to register a change in thetraffi'c controlling devices at the station, so that the system will beinitiated for the transmission of new indications as required. Alock-out relay L0 is provided at each field station to determine when aparticular field station is to transmit new indications. Relay L0 ispicked up during the initiating period of a cycle when indications aretransmitted and is stuck up until the change to normal period at the endof the cycle. The lock-out relaysupplies potential to the A and B linepulsing relays PLA and PLB so that these relays receive current only atthe station transmitting indications.

A station selecting relay S0 is picked up at all stations during theconditioning period of a cycle, when controls are being transmitted.These relays are dropped out at various stations during the codetransmitting periods, so that only the one associated with the desiredstation remains actuated after the transmission of the station selectingcode. Relays S0 and L0 control the circuits to the stepping relays sothat stepping is not efiective at those stations not in connection withthe communication circuit.

Resistance units R and R illustrated within the dotted rectangle in theupper right hand portion of Fig; 2, are of such value that a sufiicientdrop in potential isprovided for picking up a lock-out relay similar toL0 during the initiating period of an indication cycle.

A track switch T3 is operated by a switch machine SM of any suitabletype, such for example, as disclosed in the patent to W. K. Howe,1,466,903, dated September 4, 1923. This switch machin'em'ay, ifdesired, be provided with a dual control selector as disclosed forexample, in the pending application of W. K. Howe, Ser. No. 354,- 039,filed April 10, 1929, the purpose of such a selector beingto permit thelocal manual operation-orthe track switch. The position, locked andunlocked conditions of the track switch is repeated by the usual switchrepeating relay WP of the polar neutral type. This relay is controlledby a suitable circuit (not shown) so that it is energized with onepolarity or the other, depending upon the normal or reverse positions ofthe track switch. In this disclosure, it will be assumed that the polarcontact of relay WP is positioned to the right when the track switch isin its normal locked position, to the left when the track switch is inits reverse locked position and its neutral contact is dropped when thetrack switch is in mid-stroke.

The track switch has associated with it the usual detector track sectionhaving a track battery and a track relay T also suitable approachlocking and detector locking means are provided (not shown) togovern thesafe operation of the track switch in accordance with trafficconditions. It is understood that a change in the position of the trackswitch TS is repeated by the relay WP and a change in the condition ofthe detector track section is repeated by relay T The field station alsoincludes suitable bus wires, circuit connections, code jumpers and otherdevices which are necessary in operating the system, but which have notbeen completely illustrated in this disclosure for the sake of simeachcycle of operations.

plicity.

It is believed that the nature of the invention, its advantages andcharacteristic features, may be best understood with further descriptionbeing set forth in the manner of operation.

General operation The system of the present invention is shown in Figs.2, 3 and 4 in the normal or condition of rest, from which it may beinitiated into a cycle of operations, either by a manual operation, atthe control office or an automatic operation at any of the fieldstations, whenever there are new controls or new indications,respectively, to be transmitted. In the event that there are severaldifferent controls ready for transmission to field stations atsubstantially the same time, they are transmitted on separate cycles,one station for Likewise, if several field stations have indications tobe transmitted at substantially the same time, they are transmitted tothe control ofiice, one station at a time, on separate operating cycles.

It may happen that there are new controls and new indications ready fortransmission at a given time, and in this event controls are transmittedsimultaneously with the indications. On, such occasions, indications maybe transmitted from the same field station to which controls aretransmitted, or they may be transmitted from some other field station,during the same cycle of operations.

Irrespective of whether the cycle is for the transmission of controlsand/or the transmission of indications, a predetermined number ofimpulses is applied to the line circuit to accomplish the synchronousoperation of the stepping relays at the control office and at the fieldstations. These impulses are of comparatively short duration, thedeenergized or off periods of the stepping line circuit beingcomparatively shorter than the energized or on periods.

When'a cycle of operations is initiated for the transmission ofcontrols, the character of the impulses applied to the stepping line isdetermined by the particular station to be selected i and the particularcontr l t be transmitted t the selected station, in accordance with thecode jumper connectionsand the positions of the control levers,respectively, for that station.

When a cycle of operations is initiated for the transmission ofindications alone, the character of the impulses applied to the steppingline is the same for all impulses and this particular combination doesnot effect the selection of any field station, since the initiatingimpulse applied tothe stepping line is of such a character, for examplethat none of the station relays similar to S0 of Fig. 4 are picked up.When such a cycle of operations is initiated from a field station, theline circuit is energized with a series of impulses. Since such a cyclestarts out with no station relay (similar to S0 up, the impulses whichfollow are not efiective to select a station or a control device at astation.

The A and B line conductors are normally energized, the stepping lineconductor S is normally deenergized, and when controls or indicationsare initiated, start relay S'I'R in the control office is picked up,resulting in switching the battery connection so that temporarily the Sline is energized, the return circuit being by way of both the A and Blines for transmission of controls and by way of the B line alone fortransmission of indications. This period during which the battery isswitched from the A and B line conductors to include the S line isconveniently referred to as the conditioning period at the start of acontrol cycle and the initiating period at the start of an indicationcycle. Immediately following the conditioning or initiating period isthe look-out period, which is efiective to so condition the circuitsthat only one station may transmit indications to the control office atthe. same time.

After the conditioning and lock-out periods, the system continuesthrough a complete cycle of operations consisting of a number of o andon periods, this number being determined by the number of steps requiredand the number of steps in turn being governed by the size of thesystem. After the last on period, a comparatively long off ordeenergized period is effective to condition the relays for changing tonormal or the period of blank. After this change to normal period, the Aand B line conductors are again energized by current from battery B,which restores the system to the normal period.

For convenience in describing the operation of the present invention, anoperation chart is shown in Fig. 5. In the upper portion of this chartthe important functions of the system during a control cycle areillustrated, while the lower portion illustrates the important functionsof an indication cycle. Referring to the chart illustrating a controlcycle, the normal period is shown at the extreme left and during thisperiod line S is deenergized or open, as indicated by referencecharacter 0. Line A is energized with potential and line B withpotential as illustrated. It is during this period that the system ismanually started by an operation in the control office. This normalperiod is an off period since line S is deenergized.

During the next or conditioning on period, line S is energized withpotential, the return circuit being by way of lines A and B as indicatedby the reference characters. It is during this on period that all relayssimilar to S0 are picked up.

From the beginning of the conditioning period, up to and including theend of the cycle is conveniently referred t oas'the operatin'glcycl'e';The beginning of the first off period and the' end of the third "onperiod is bounded by what may be conveniently referred to asthe'transmitting period. 'f

The transmitting period 'is'divided into off and on periods and sincethe present disclosure shows only three steps, the first, second andthird off and on-"periods are indicated in this'chart. It will beunderstood that additional steps, when provided, are insertedbetween'the third on period and the change to normal period.'- o a c Theindication cycle chart shown in the lower portion of Fig. 5 comprises anormal period followed by an operating cycle divided into initiating,lock-out, conditioning, transmitting and change to normal periods. Thetransmitting period is divided into off and on periods, with these offand on periods subdivided as indi cated. For want of space, the thirdofi" and on periods of the indication cycle have not been included butit will be understood that they are similar to preceding periods.

'An'analysis of a duplex cycle has not been provided since such a cycleis merely a combination of control and indication cycles. During duplextransmission, impulses of distinctive character are placed on line S foroperating the apparatus at the control office and at the field stations,the character of these impulses determining the selection of the stationand thereafter the control device at the station, The A and. B lines areconditioned foi the return circuit in accordance with the indicationcode combinations to be transmitted from 'the field station to thecontrol oflice in the same manner as when indications alone aretransmitted.

- Detailed operation Normalper'iod.-With the communication part of thecentralized traflic controlling system, with which thisinventionis'concerned at normal, most of' the "relays in the controlofiice and at the field stations are in their normal or 'deener'gizedpositions. The exceptions are relays MA, MB, MAP and MBP in the controloflice and relay VPC at the field station. Relays MA and MB areenergized by current flowing from battery B over the A and. B lines inseries and, as" indicated in the operation chart under normal period,potential is applied to the A line and potential to the B line.'Referring to Fig. 2, this circuit may be traced from the terminal ofbattery B, back contact ID of relay STR, winding of relay MA, A line II,back contact I50 of relay PLA of Fig. 4, over the A line conductor I5Iextending through all of the field stations in series, including backcontacts of other A line impulsing relays such as PLA resistance coils Rand R in series, located at the last station, back contacts of the Bline impulsing relays such as PLB B line conductor I52, back contact I53of relay PLB B line I2, winding of relay MB and back contact I3of relaySTR to the side of battery B. The circuit for energizing relay MAPextends from front contact I28 of relay MA and lower winding of relayMAP,'to The energizing circuit 'for relay MBP extends from front contactI29 of relay MB and lower windingyof relay MBP, to

The circuit for energizing relay VPC extends through back contacts I90and I95 of relays PLA and PLB respectively.

At the field station, the change repeating relay CHP is" "normallypicked 'up over circuits (not shown), track relay T is normally pickedup by a"circuit (not shown) energized by the track battery and'relay WPis normally energized, with its polar contacts to the right, by means ofa circuit (not shown) which is controlled by the switch machine.Although these circuits for controlling relays CHP T and WP have notbeen included in the drawing of Fig 4, it will be readily under stood by'those skilled in the art how they are conditioned by'the' difierentdevices at the field station.

Manual starting.With the system in its normal condition, it will beassumed that the operator in the control office desires to transmitcontrols to a particular field station, such as the one illustrated inFig. 4. When the starting button SB is actuated, a suitable storingrelay is positioned and the CD relay associated with the desired stationis picked up. The actuation of the CD relay closes a circuit for pickingup relay C, extending from back contact I4 of relay SA, back contact I5of relay NC, front contact I8 of relay CD and winding of relay C, toRelay C closes a stick circuit for itself extending fror'n' back contact6 of relay SAP, front contact 68 and winding of relay C, to

The operation of relay C opens the pick-up circuit of relay FC at backcontact H, which prevents the picking up of relay FC after the cycle isinitiated by a manual start in the control office. This gives thecontrol ofiice' priority, since relay C can be picked up with relay SAdown, while relay FC can not be picked up until relay SAP is down. Thus,a time interval is introduced between the dropping of relay SA and thedropping of relay'SAP, when the system advances through the change tonormal period during which the control oihce may take control of thesystem.

If a field station attempts to start the cycle by picking up relay FC atthe same time the control oflice starts the cycle, the actuation ofrelay C prevents the picking up of relay FC so that the control oflicegets first choice of the system. If the field station start occursslightly in advance of the control office start, relay FC is picked up,which energizes relay NC so that relay C can not thereafter be picked upduring this same cycle, because the pick-up circuit of relay C is openedat back contact I5.

The actuation of relay C closes a circuit for picking up relay STR,extending from front contact I8 of relay C and winding of relay S'I'R,to Relay C also closes a circuit for picking up relay PC, extending fromback contacts I9, 20 and 2I in series of relays 3V, 2V and IV, frontcontact 22 of relay C, bus 23, back contact 24 of relay FC' and windingof relay PC, to

This is the conditioning period. The energization of'relay PC causes theS line to be energized with potential, while the A and B lines areenergized as indicated in the conditioning period of the operationchart. The circuit for energizing the line conductors extends from theterminal of battery B, front contact I of relay STR, front contact 25 ofrelay PC, back contact 26 of relay NC, winding of relay F, back contact21 of relay EP, Sline conductor 28, winding of relay F of Fig; 2,windings of other line relays similar to F at other field stations,resistance coils R and R, at the last field station, back contactsof'relays such as PLA and PLB at other field stations, A and B lineconductors II and I52, backcontacts I50 and. I53 of relays PLA and PLBrespectively, A and B lines II and I2, windings of relays MA and MB andthence from the Winding of relay MB through back contact I of relay NCand front contact 8 of relay PC to the terminal of battery B. The A lineconductor circuit extends from the winding of relay MA through frontcontact I3 of relay STR, back contact I of relay NC and front contact 8of relay PC to the terminal of battery B.

The stepping line conductor S being energized causes relay F in thecontrol office and relay F at the field stations to be positioned to theright. Relay F closes a circuit for actuating relay FP extending fromcontact 29 of relay F in its right hand dotted position and winding ofrelay F'P, to Relay F closes a circuit for picking up relay FP extendingfrom contact I54 of relay F in its right hand dotted position andwinding of relay FP to The actuation of relay FP in the control officecloses a circuit for picking up relay SA, extending from front contact30 of relay FP and winding of relay SA, to The operation of relay SAcloses a circuit for picking up relay SAP, extending from front contact3| of relay SA and Winding of relay SAP, to

Referring to the field station, the actuation of relay FP opens its backcontact I55 which disables the pick-up circuit of relay PLA extendingthrough back contact I56 of relay SA and back contact I5'I of relay CHPto the lower Winding of relay PLA which pick-up circuit is effective tostart a cycle of operations from a field station. It Will thus be seenthat as. soon as relay FF is picked up and its contact I55 opened, nofield station can obtain access to the line for transmission ofindications.

The picking up of relay FP also closes a circuit for picking up relay S0extending from back contact I58 of relay SA front contact I59 of relayFP contact I66 of relay F in its right hand dotted position, backcontacts I6I, I62 and I63 in series of relays 3V 2V and IV control busI64 and lower winding of relay S0 to At this time, relays similar to S0at all other stations are picked up by means of similar circuits, but aswill be specifically pointed out during the detailed description, theserelays are dropped out at the other stations, while the one illustratedinFig. 2 is maintained energized.

The actuation of relay FP also closes a circuit for.picking up relay SAextending from front contact I55 of relay FP and winding of relay SA toThe operation of relay SA interrupts the above described pick-upcircuitof relay S0 but it is not released since a substitute circuit isclosed for holding relay S0 which extends from make-before-break frontcontact I58 of relay SA front contact I 65 of relay S0 contact I60 ofrelay F in its deenergized position and the remainder of the circuitabove described, to the lower winding of relay S0 Referring back to thecontrol office, the actuation of relay SAP closes a circuit for pickingup relay EP which extends from front contact 32 of relay SAP, backcontact 33 of relay E and lower winding of relay EP, to It will bementioned here that the purpose of front contact 9 of relay EP is toshort circuit the upper winding of this relay when it is actuated whichhas the effectof rendering this relay quick to pick up and slow torelease for obtaining the desired timing of the stepping operation. Theactuation of relay EP opensthe stepping line circuit, at back contact21, which advances the cycle into the first off period.

Polarity selection of impulses-As above pointed out, the first impulsein line S is when a cycle of operations is started from the controlofiice. This is indicated in the chart under the conditioning period andis due to the fact that control relay PC is picked up at the start of acontrol cycle.

When line S is deenergized, by relay EP opening its contact 21 toadvance the system into the first off period, relay F is released and byopening its contact 29, causes the release of relay FP. As will bespecifically pointed out later on in the description, stepping relay IVis picked up during the first off period. This is effective to conditionthe No, 1 control, by selecting the polarity to be appliedto line Sduring the first on period. This conditioning circuit holds relay PC inits actuated position and extends from back I contacts 35 and 36 ofrelays 3V and 2V,front contact 31 of relay IV, No. 1 code bus M, frontcontact 38 of relay CD, code jumper connection 39, bus 23, back contact24 of relay FC and winding of relay PC, to This connection of codejumper 39 to the bus selectively conditions the first control impulse Ifcode jumper 39 were connected to the bus 47, then relay NC would bepicked up instead of relay PC, thus providing a impulse-for the No. 1controls The control of the PC and NC relays is effected during otheroff periods by means of other code jumpers such as jumper 40. Thus, inthe second off period, relays 2V and VP will be up and the selection ofthe or bus, by means of jumper it, is extended by way of front contact4| of relay CD, No. 2 code bus 45, front contact 36 of relay 2V and backcontact 35 of relay 3V to so that relay PC will be again picked up ifcode jumper 46' connects to the bus. However, in the present embodimentit is assumed that the No. 2 code jumper 46 connects to the bus, so thatrelay NC is picked up terminal of battery B through back contact ll ofrelay PC and front contact 26 of relay'NC to the S line. The terminal ofbattery B is con nected to the A and B line conductors over circuitsextending through front contact I!) of relay STR, back contact 25 ofrelay PC, front contact I of relay NC to the B line and through frontcontact I 3 of relay STR to the A line.

During the third off period, it will be assumed that relay 3V is up asindicated in the operation chart. The No. 3 control is conditionedduring this period by dropping relay NC and picking up relay PC, sincethe polarity of the third on period is assumed to be in the S line.Relay NC is dropped when the No. 2 code bus 45 is opened at back contact35 of relay 3V and relay PC is picked up when the No. 3 code bus 46 isclosed from front contact 35 of relay 3V, No. 3 code bus 46, frontcontact 42 of relay CD, contact 43 of switch machine lever SML, assumedto be in its right hand position, bus 23, back contact 24 of relay FCand winding of relay PC,-to The actuation of relay PC selects apotential to be applied to line S during the third on period.

It willbe apparent that a impulse would be conditioned during the thirdoff period and applied to the S line during the third on period if leverSML should be in its left hand dotted position, because this wouldextend the above traced circuit to relay NC instead of relay PC. Fromthe above it will be observed that different code combinations may bechosen for selecting different stations, by arranging the jumperconncctions 39 and 40 in different positions, but with these jumpersarranged as shown in Fig. 2, the two impulses applied to the line forselecting the station are for the first impulse and for the secondimpulse. It will also be obvious that while only two steps are indicatedfor making station selection, additional steps and associated codejumpers may be provided in systems requiring a larger number of codecombinations. It will also be understood that more than one step may beprovided for selecting additional control devices, similar to lever SML,but it is believed that the typical arrangement disclosed is sufiicientto illustrate the complete functioning of the system.

From the above it will be seen that the impulses applied to the linecircuit during a control cycle always begin with a and a combination ofand impulses follow. These following impulses are dependent upon thecode jumper connections and the control lever positions, made effectiveby the particular code determining relay CD which is picked up duringthe control cycle. Also, the character or polarity of the impulses inthe stepping line circuit is selected by polarity determining relays, PCfor a impulse and NC for a impulse and these polarity determining relaysare positioned during the off periods, in readiness for the applicationof the preselected polarity during the following on periods.

Line pulsing and operation of stepping relays. It has been mentionedthat the impulses which follow the conditioning period Vary in polarityand with the code jumpers and switch machine lever conditioned as shownin Fig. 2, the impulses in the S line energize this line during thethree on periods with and polarities. Irrespective of the particularpolarities with which line S is energized, relay F? in the controloffice and relay FP at the field station repeat the operations of relaysF and F Relay IV in the control oflice is picked up during the first offperiod by means of a circuit extending from front contact I4 of relaySA, back contact 48 of relay FP, back contact 49 of relay VP, backcontact 50 of relay 2V and winding of relay IV, to The operation ofrelay IV closes a stick circuit for itself extending from front contactI4 of relay SA, stick conductor 64 and front contact 5I of relay IV tothe winding of relay IV. When relay IV is picked up, a circuit iscompleted for picking up relay E, extending from back contact I9 ofrelay 3V, back contact 20 of relay 2V, front contact 2I of relay IV,back contact 34 of relay VP and Winding of relay E, to Relay E opens itsback contact 33 which allows relay EP to drop and.

" again energize line S.

This is the first on period. Relays F and FF are now picked up in turnand relay FP closes a circuit for actuating relay VP extending fromfront contact 32 of relay SAP, front contact 52 of relay FP, frontcontact 53 of relay MBP, front contact 54 of relay MAP, back contact 55of relay 3V, back contact 55 of relay 2V, front contact 51 of relay IVand. winding of relay VP, to Relay VP establishes a stick circuit foritself extending from front contact 32 of relay SAP, front contact 58 ofrelay VP and over the remainder of the above described actuatingcircuit, to the winding of relay VP. This stick circuit for relay VP iseffective until stepping relay 2V is picked up and opens contact 56,which occurs during the second off period. For maintaining relay VP inits actuated condition during the second off period, an additional stickcircuit is established extending from front contact 32 of relay SAP,back contact 59 of relay MBP or back contact 60 of relay MAP or backcontact 52 of relay FF and front contact SI of relay VP, to the windingof relay VP.

Relay VP, in picking up, opens the circuit of relay E at back contact34, so that relay E drops after a short time interval and closes thecircuit for picking up relay EP, which has been described. This advancesthe system from the first on period into the second off period, sincethe actuationof relay EP opens its contact 21 and deenergizes the S lineas well as the A and B lines.

This is the second off period. Relays F and FP are dropped and a circuitis established for picking up relay 2V extending from front contact I4of relay SA, back contact 48 of relay FP, front contact 49 of relay VP,back contact 62 of relay 3V, front contact 63 of relay IV and winding ofrelay 2V, to Relay 2V closes its own stick circuit to stick conductor 64by way of its front contact 65. A circuit is now closed for picking uprelay E, extending from back contact I9 of relay 3V, front contact 20 ofrelay 2V, front contact 34 of relay VP and Winding of relay E, to RelayE opens its back contact 33 which allows relay EP to drop and energizethe S line at its back contact 21. This advances the system out of thesecond off period.

This is the second on period. Relays F and FF are again energized andrelay VP is dropped during this period, since its pick-up circuit isopen at back contact 56 of relay 2V and its stick circuit is open atback contacts 52 of relay FP, 59 of relay IVIBP and 60 of relay MAP. Thecircuit of relay E is now interrupted at front contact 34 of relay VP,allowing relay E to drop and establish the pick-up circuit for relay EPwhich has been previously described. Relay EP picks up and deenergizesthe S line and the A and B lines, which advances the system out of thesecond on period.

This is the third off period. Relays F and PP are again dropped and acircuit established for picking up relay 3V, which extends from frontcontact I4 of relay SA, back contact 48 of relay FP, back contact 49 ofrelay VP, front contact 50 of relay 2V and winding of relay 3V, to Relay3V closes a stick circuit for itself to stick conductor 64 by way of itsfront contact 66. A circuit is now established for picking up relay E,extending from front contact I9 of relay 3V, back contact 34 of relay VPand winding of relay E, to Relay E opens its back contact 33 whichallows relay EP to drop and close the energizing circuit for the lineconductors to advance the system out of the third off period.

This is the third on period. Relays F and FP are again picked up and acircuit is established for picking up relay VP which extends from frontcontact 32 of relay SAP, front contact 52 of relay FP, front contact 53of relay MBP, front contact 54 of relay MAP, front contact 55 of relay3V and winding of relay VP, to Relay VP again closes a stick circuit foritself which is effective untilthe system advances through the change tonormal period and which extends from front contact 32 of relay SAP,front contact 58 of relay VP and front contact 55 of relay 3V, to thewinding of relay VP. The circuit of relay E is now open at back contact3 5 of relay VP, which allows relay E to drop after a short timeinterval and establish the pick-up circuit for relay EP. Relay EP isactuated and opens the S line circuit at its contact 2i, whichdeenergizes the line conductors and advances the system out of the thirdon period.

This is the change to normal period. Relays F and PP are dropped andsince there are no more stepping relays to be picked up during this offperiod, relay E can not be picked up and relay EP can not be dropped, inthe manner described for the previous off periods. This results'inrelays F and PP remaining down for a sufiicient time to allow relay SAto drop, which opens its front contact i i and allows all the steppingrelays to be restored to normal. Relay SA opens its front contact 3iwhich deenergizes relay SAP which releases and by opening its frontcontact 32, causes the release of relay VP. Relay SAP, in opening itsfront contact 32, also opens the circuit of relay EP allowing this relayto drop.

Relay SA, in releasing, opens its front contact (all which deenergizesthe stick circuit of relay C allowing this relay to be released and byopening its front contact it the circuit of relay STR is interrupted andrelay STR restores to normal. The S line conductor is deenergizedshortly after the dropping of relay SA and before the release of relaySAP causes relay EP to release and close its contact 2?. The A and Bline conductors are again energized with potential on the A line andpotential on the B line, as indicated in the second part of the changeto normal period. Relays MA, MB and their repeating relays MAP and MBPare now picked up and the system is advanced into its normal period withthe A line conductor still energized. (-1-) and the B line conductorenergized It is to be understood that these circuit connections may beextended for as many steps as desired, with the pick-up and stickcircuits of the stepping relays and the steering relay extended inanobvious manner. It has already been mentioned that the stepping relaysand the steering relays at the field stations operate in a substantiallyidentical manner and for this reason it is not believed necessary todescribe the operating and pick-up circuits of these relays in detail.Relays iV 2V and 3V of Fig. 4 are picked up in synchronism with relayslV, 2V and 3V of Fig. 2. The pick-up circuits of the stepping relaysshown in Fig. 4 extend from front contact itt of relay SA back contactlfil of relay FP (which operates in synchronism with relay FP in thecontrol office) and front contact W8 of relay S during the transmissionof control impulses. The extension of this circuit to the stepping relaywindings is through back and front contacts liiil of relay VP whichcircuits are simi" lar to those of Fig. 2.

As will be later explained, some of the relays similar to S0 at otherstations are dropped out, which is effective to open. their contactssimilar to ltil and at these stations the stepping circuits areinterrupted, so that stepping does not continue throughout the cycle atsuch stations. During the transmission of indications when no relaysimilar to S0 is picked up, front contact iii] of relay L0 is effectiveto complete the pick-up circuits of the stepping relays.

From the above description and by referring to the operation chart, itwill be observed that the stepping relays are picked up in rotationduring successive off periods and the steering relays are shifted duringthe on periods. The steering or half step relays VP and VP pick upduring the odd on periods and release during the even on periods.

Contacts 59 and All of relays MBP and MAP of Pig. 2, connected inmultiple with back contact 52 of relay PP, are for the purpose ofpreventing the release of relay VP during the even on periods, untilrelays MBP and MAP are picked up. The purpose of contacts 53 and d ofrelays MBP and MAP, in series with front contact 52 of relay PP, is toinsure that relays MBP and MAP are picked up at the beginning of the odd,on periods before relay VP can be picked up. These four contacts onrelays MBP and MAP therefore serve the purpose of holding back theshifting of relay VP until the relays, which are to be conditioned overthe line conductors, are properly positioned.

During the change to normal period, the stepping relays and the steeringrelay of Fig. 4 are released in a manner similar to those in the controloffice, when relay SA drops and opens its front contacts M56 and ill.

The purpose of relay VPS is to prevent the shifting of relay VP untilthe relays in the line even on"- period until-relay VPC picks up andopens its back contact H3. Relay VPC can not pick up until both the Aand B line impulsing relays PLA and PLB- are down. Therefore, relay VPcan not drop until both the A and B line conductors are conditioned byrelaysPLA and PLB during the even on periods. Similarly, relay VP cannot be picked up during the odd on periods until relay VPC picks up andcloses its front contact H4 and relay VPC as above mentioned, can notpick up until both relays PLA and PLB are down. This insures that therelays at the field station in the A and B line conductors will be intheir proper positions, as well as the relay in the S line conductor,before relay VP can be shifted.

Transmission of controls-It will now be assumed that the stepping relaysin the control office and at the field station illustrated in Fig. 4,together with the respective steering relays, operate as above describedand an explanation will be given of the circuits which are effectiveduring this operation to transmit controls.

As above explained, line S is conditioned with a impulse for picking uprelays. similar to S0 at all field stations and during this conditioningperiod, relays SA and SAP in the'control office and relays similar to SAat the field stations are actuated.

It is assumed that the impulse applied to line S during the first onperiod is determined all others are to be dropped out. At those stationshaving a jumper similar to I15, relays similar to S0 will be maintainedenergized during the first on period by means of a circuit similar tothat extending from front contact I58 of relay SA front contact I65 ofrelay S0 contact I60 of relay F in its right hand dotted position, backcontact I6I of relay 3V back contact I62 of relay 2V front contact I63of relay IV code jumper I15, bus I64 and lower winding of relay S0 to Atthose stations not 'having a code jumper similar to I15 connected to busI64, the relays similar to S0 are dropped.

When the system advances into the second off period, those relayssimilar to S0 which are up will be stuck up over a circuit similar tothat extending from front contact I58 of relay SA front contact I65 ofrelay S0 contact I60 of relay F in its deenergized position, frontcontact I11 of relay SO and upper winding of relay S0 to It is of courseobvious that the stick circuits of those relays similarto S0 which aredropped during the first on period, are not completed during the secondoff period, since their contacts similar to I11 are open.

The system now advances into the second on period by means of a impulseapplied to line S, which was conditioned during the second off period ina manner which has already been explained. Relay 2V is up and relay VPis down during this period and a circuit is completed for holding relayS0 in its operated position, which extends from front contact I58 ofrelay SA front contact I65 of relay S0 contact I60 of relay F in itsleft hand dotted position, back contact I19 of relay 3V front contact Iof relay 2V code jumper I8I, bus I64 and lower winding of relay S0 to Itwill be understood that, in the embodiment disclosed herewith, only therelay SO illustrated in Fig. 4 will be maintained energized during thisperiod, since it is assumed that only two stepping relays are used forstation selection. With two steps for station selection, four stationsmay be selectively chosen by dropping out one half of the stations onthe first step, which leaves two relays similar to S0 picked up. On thesecond step, one half of the remaining relays similar to S0 will bedropped, leaving only one (which is assumed to be that one illustratedin Fig. 4) in its actuated position.

During the third off period, relay 3V is picked up and relay S0 is stuckup over the above described circuit, including its front contact I11 andmake-before-break contact I60 of relay F in its deenergized position. Assoon as relay 3V is picked up, potential isconnected through its frontcontact I82 to the stick circuit of relay S0 so that this relay ismaintained energized during the remainder of the stepping impulses. Withrelay S0 stuck up after station selection, additional impulses areeffective to operate only those stepping relays at the stationillustrated in Fig. l, since the-circuit for these relays is by way offront contact I68 of relay S0 at the one station illustrated.

During the third on period, which occurs after station selection, theNo. 3 control is executed by actuating relay F of Fig. 4 to the right. Acircuit is now closed for actuating switch machine relay SMR to theright, which extends from front contact I5 8 of relay SA front contactI65 of relay S0 contact I60 of relay F in its right hand dottedposition, front contact I6I of relay 3V and upper winding of relay SMRto With relay SMR positioned to the right,

a circuit is closed from contact I84 of relay SMR in its right handposition and normal operating winding of switch machine SM to (ON) Thisresults in operating the switch machine in such a direction that switchTS is advanced to its normal locked position.

It will be noted that in the event of a impulse during the third onperiod, relay F would be positioned to the left and the above describedcircuit for operating relay SMR would be extended by way of contact I60of relay F in its left hand dotted position, front contact I19 of relay3V and lower winding of relay SMR to This would result in positioningrelay SMR to the left and by closing its contact H36 in its left handdotted position, would energize the switch machine in the oppositemanner for moving the track switch TS to the reverse locked position.

In brief, the positioning of control lever SML determines the polarityapplied to the switch machine control relay SMR which in turn governsthe operation of the switch machine. Obviously, if the control lever ismoved to a position out of correspondence with the track switch TS thistrack switch will be operated, but if the control lever is in a positionwhich corresponds with the position of the track switch, the trackswitch will remain in its former position.

Although no signal relays or other control devices, other than relay SMRhave been shown, it will be understood that the step-by-step operationof the stepping relays may occur in sequence and in synchronism for asmany steps as required to transmit controls to such other signal relaysor other devices as desired.

This transmission'of controls continues until the predetermined numberof steps have been taken, which by way of example, has been specificallyillustrated as including three steps, two of which have been employedfor station selection, followed by one which is employed fortransmission of controls after station selection.

End of control cycZe.It has been explained that relays F, FP, SA, SAPand all stepping relays in the control ofiice are released during thechange to normal period which follows the third on period. It will berecalled that the change to normal period is long compared with other01f periods, resulting in relays F and FP in the control ofiice andrelays F and FP at the fieldstation being down for a time intervalsufiicient to allow relays SA and SAP in the control oflice and relay SAat the field station to be released. The stepping relays and theassociated steering or half step relay at the field station release whenrelay SA drops and opens its contacts I66 and I 1 I. The stick circuitof relay S0 including its front contact I11, is interrupted when relay3V drops and opens its front contact I82 and since relays FP and SA aredown at this time, there is no circuit for holding relay S0 and it isdropped.

Simultaneously with the dropping away of the stepping relays in thecontrol oflice, the particular code determining relay CD which waspicked up during the cycle, is deenergized so that the next codedetermining relay in order may be effective at the begining of the nextcycle, if its corresponding starting button has been actuated and thiscondition stored by a storing relay (not shown).

The release of relay SA in the control ofiice breaks the energized stickcircuit of relay C which extends through its front contact 68 so thatrelay C drops and b'y'op'en ing its front contact l8, causes the releaseof relay STR.

Automatic start by a field station.-'Whenever the system is in thenormal period or period of f blank, it may be initiated from a fieldstation,

from a normal position to a reverse position in response to a controltransmitted by lever SML, in a manner previously explained. When thetrack switch responds to such a control signal, it causes relay WP todeenergize during the transition period, when the switch is shiftingfrom normal to reverse, after which relay WP is energized with oppositepolarity. The deenergization of relay WP as well as its reenergization,

momentarily interrupts the stick circuit of a change relay in a mannerwhich is not shown in Fig. 4 but which is well known in the art, and isshown, for instance, in the patent to De Long and Plank No. 1,852,402,dated April 5, 1932. Relay CI-IP is dropped as a result of such a changeat the field station.

Relay CHP may also be released upon a change in traffic conditions, suchfor example, as the deenergizationof track relay T when a train passesover the associated detector track circuit, in accordance with the usualpractices. In brief, the stick circuit for the change relay is carriedthrough front and back contacts of the WP relay, the T relay and may besimilarly carried through like contacts of other trafiic controllingdevices associated with the field station.

Irrespective of the particular change which occurs, it results indropping the change repeating relay CHP which closes a circuit forpicking up relay PLA extending from back contact I55 of relay FP backcontact I56 of relay SA back contact Iil'l of relay CHP and lowerwinding of relay PLA to Relay PLA closes a stick and MBPin the controlofiice.

Referring to the indication cycle portion of Fig. 5, the system is nowin the first part of the initiating period with all three lineconductors deenergized as indicated by reference character (open)associated with all three lines. The

release of relay MAP closes a circuit for pickingup relay FC extendingfrom back contact ii! of relay MAP, back contact 69 of relay SAP, fieldstart conductor 'lI, back contact ill of relayC, back contact E2 ofrelay STR and winding of relay FC, to Relay FC, which is operated onlyduring a cycle which is initiated at a field station, prevents thepicking up of relay PC during such a cycle, by opening the circuit ofrelay PC at back contact 24. 'Relay FC closes a stick circuit for itselfextending from back contac 6 of relay SAP, front contact 19 and windingof relayFC, to A circuit is now completed 7 for picking up start relaySTR, extending from front contact 13 of relay FC and winding of relaySTR, to A circuit is also closedfor picking up relay NC, which extendsfrom back contact 14 of relay C, front contact I of relay FC and windingof relay NC, to

Since this is a cycle for the transmission of indications alone, all ofthe impulses applied to the S line are because relay NC is held in itspicked up position throughout the cycle. Relay NC opens its back contactI5, which is effective to prevent the control office breaking in on theconnection after the communication system has been initiated from afield station. The operation of relay STR closes a circuit forenergizing the S line conductor with potential, which extends from theterminal of battery B, back contact 8 of relay PC, front contact '26 ofrelay NC, winding of relay F and back contact 2? of relay EP to line 28.

This is the second portion of the initiating period with line Senergized the A line open (O) and the B line energized as indicated inthe operation chart. The potential, applied to the 8 line conductor 28,extends from the control ofiice through relay F at the field stationshown in Fig. 4, through relays F at other field stations, resistancecoils R and R at the last field station, back contacts of relays such asPLB at other field stations, conductor I52, back contact I53 of relayPLB B line conductor I2, winding of relay MB, front contact I of relayNC, back contact of relay PC and front contact I I) of relay STR to theterminal of battery B. The circuitv branches from resistance coil R andleads through back contacts such as PLA at other stations, conductorI5I, front contact I of relay PLA ,-lower winding of lockout relay L0back contact ISI of relay SA to the B line conductor I2 and thence byway of theremainder of the circuit just traced to the terminal ofbattery B.

It will be noted from the above traced circuit that the A line conductorII is open toward the control oifice, at back contact I56 of relay PLAat the station initiating the call. The A line conductor I5I extendingtoward stations farther away from the control oiiice, is connected tothe B line conductor at the station initiating the call through thelower winding of relay L0 The resistance coils R and R provide asufficient drop, in the A. and B line conductors, extending from thestation shown in Fig. 4 to the end of the line, so that the lowerwinding of relay L0 is not short circuited, but receives sufficientpotential across the terminals of its winding to cause it to beenergized.

With the system in the second part of the initiating period and withline S energized line A extending to the control office deenergized andline B energized relays F, MB and MB? in the control ofiice are pickedup and relay Fl at the field station is positioned to the left. Relay FPin the control office and relay FP at the field station are picked upover circuits closed by contacts 29 and I54 of relays F and Frespectively. Relay L0 is picked up by means of current flowing in lineconductor I5I, as above described.

The system is now in the lock-out period. Relay SA in the control officeis picked up over its previously described pick-up circuit and a circuitis closed for sticking relay MBP, extending from front contact M ofrelay SA, stick conductor 64, back contact ll of relay E, front contactE8 of relay MBP and upper winding of relay MBP, to An additional stickcircuit is 75 closed, for relay FC extending from front contact 61 ofrelay SA, front contact 19 of relay FC and winding of relay FC, to

Relay SA at the field station is picked up by a 5 circuit completed atfront contact E55 of relay G FP With relays FP or SA up, no other relaysimilar to FLA can be picked up because the pick-up circuit is open atback contacts similar to 155 or I56. Relay SA closes a stick circuit gfor relay LO extending from front contact I93 of relay SA front contact194 of relay L and upper winding of relay L0 to The picking up of relaySA opens the pick-up circuit of relay PLA at back contact I56 and thestick circuit of relay PLA at back contact I88 so that relay PLA isdropped.

The system is now advanced into the conditioning period. The A lineconductor is now energized, due to the current in conductor l5i,

gg through back contact I50 of relay PLA A line conductor 1 l, windingof relay MA, front contact l3 of relay STR, front contact I of relay NC,back contact of relay PC and front contact H] of relay STR to theterminal of battery 5 B. As shown in the operation chart, during theconditioning period line S is energized and lines A and B Relays MA andMAP in Fig. 2 pick up when the A line is energized during this periodand gg relay MAP establishes a stick circuit for itself, ex-

"tending from on stick conductor 64, back contact H of relay E, frontcontact 80 of relay MAP and upper winding of relay MAP, to Relay SAP ispicked up when relay SA closes its 5 front contact 31. Relay VPC of Fig.4 is again picked up when relay PLA releases by means of a circuitextending from back contact I99 of relay PLA back contact I95 of relayPLB and Winding of relay VPC to Relay EP 4? of Fig. 2 is picked upduring the conditioning period, over a circuit extending from frontcontact 32 of relay SAP, back contact 33 of relay Eand winding of relayEP, to Relay EP opens the S-line conductor at its back contact 21, whichdeenergizes the three line conductors '28, II and I2.

The system is now advanced into the first off period. The steppingrelays and their associated steering relays in the control office and atthe 5 field stations are operate-d during an indication cycle, in thesame manner as previously described in connection with a control cycle,so that the detailed description of this operation will not be repeated.The line conductor S is impulsed by relay EP in the same manner aspreviously de- 'scribed so that this operation will not be againexplained. The relays similar to S0 at the field stations are not pickedup during an indication cycle, because the conditioning impulse is 60which actuates relay F to the left so that their pick-up circuits arenot effective. Relay L0 however, is picked up as above described andcompletes a circuit for the stepping relays by way of its front contactI10.

65w Registration of a field station-4t will now be 'assumed that thesystem is advanced through the transmitting period and the change tonormal period, the transmitting period including first, second and thirdoff periods and first, second 70 and third on periods.

One of the features of the present invention resides in means forobtaining an increase in the number of indications which may betransmitted during an operating cycle. It is believed that 7 thisfeature may be best understood by assuming that the field station shownin Fig. 4 is assigned indication code combination as indicated in thestation registration period at the lower part of the indication cycle ofFig. 5. The above assumption means that the No. 1 off indication isexecuted because relay MX is down, connecting (B) to the No. 1 offindication bus. The No. 1 on indications are exeouted and because relayMAP is down, connecting (B) to the No. 1A on indication bus and relayMZBP is up connecting (13+) to the No. IE on indication bus.

It will be noted that this station registering code is obtained withonly one step of the stepping relay bank. The choice during the offperiod is or and the choice during the on period is or or a total offive choices. This does not mean that the line circuits are energizedand but is simply a convenient manner of indicating the differentcombinations obtained. The choice of or off refers to relay MX up anddown respectively. The on choices refer to relays MAP down and MBP up,relays MAP up and MBP down and relays MAP and IVEBP up, respectively,all as determined by the combinations of the A and B lines for thereturn circuit for line S.

It has been explained how the system is advanced into the first offperiod during an indication cycle. The stepping line S and the returnlines A and B are all deenergized during the first off period, resultingin the picking up of relays IV and l V in the manner previouslydescribed. Relays F and FF are dropped during the first off period andrelays MAP and MBP are stuck up by means of a circuit extending fromfront contact 54 of relay SA, stick conductor 64, back contact ill ofrelay E and front contacts and T8 of relays MAP and MBP respectively, tothe windings of these relays.

Relay E is picked up during the second part of the first off period,which opens the above described stick circuit of relays MAP and MBP andthese two relays are released. Relay MX is not picked up during thisperiod because the pick-up circuit through its lower winding is open atback contact lei! of relay MBP, when these relays are up and at frontcontact 8! of relay MAP when they are down.

When relay W of Fig. 4 picks up during the first off period, a circuitis completed for pick ing up relay PLA which extends from back contactI55 of relay FP front contact I56 of relay SA off indication bus I91,code jumper l fi, No. 1A ofi indication bus 200, front contact 2% ofrelay IV back contact 201 of relay 2V back contact 268 of relay 3V backcontact 269 of relay 'v'P upper winding of relay PLA and front contact5% of relay L0 to Relay PLB is down during this off period because theNo. 113 on? indication bus Zlll is not energized.

The system is next advanced into the first on period by the dropping ofrelay EP in the control office and the energization of line S. Thereturn circuit is by way of line B alone because relay PLA is up, whichopens line A at its back contact I 5|]. With the return circuitextending over line B, relays F, FP, MB and MBP are picked up in thecontrol ofiice. With relay MAP down and relay MBP up, there is nocircuit for picking up relay MX so that the No. 1 off indication isconditioned by relay MX remaining down and connecting (B-) to the No. 1off indication bus 89, to be executed as will be later described.

With relay PLA up, the circuit of relay VPC is open at back contact I90so that relay VPC is dropped. During the first-part of the first onperiod, relays F and FP at the field station are picked up, whichresults in disconnecting potential from the off indication bus ill! atback contact I55 of relay FP Relay PLA- is therefore released during thesecond part of the first on period, which results in energizing the Aline and picking up relays MA and MAP in the control ofiice. Relay MXcan not be operated under this condition because it requires relay MAPup and relay MBP down to energize the pick-up winding of relay MX. Bothrelays MAP and MBP are now up.

When relay PLA drops at the field station, the circuit of relay VPC isagain completed and this relay is picked up. With relays FP, MAP AND MBPup in the control office, the circuit is completed for picking up relayVP which has previously been described. With relay VPC up at the fieldstation, the circuit is complete-d for picking up relay VP which extendsfrom front contact ill of relay SA front contact I86 of relay FP frontcontact I'M of relay VPC back contact 58'! of relay 3V back contact 222of relay 2V front contact 223 of relay IV and winding of relay VP to Itwill thus be evident that the combinatio indicated in the operationchart for the second part of the first on period, that is, line S andlines A and B is used to control the picking up of relay VP in thecontrol office and relay VP at the field station in synchronism. Thisfeature is provided as a means for synchronizing the steering or halfstep relay operation at the control ofiice and at the field station.

With the VP and VP relays up, the system is advanced into the third partof the first on period by picking up relay PLA over a circuit extendingfrom code jumper I98, No. 1A on indication bus 2%, front contact Zlil ofrelay IV back contact 2H of relay 2V back contact 212 of relay 3V frontcontact ace of relay VP upper winding of relay PLA and front contact I99of relay L0 to Relay PLA is picked up because code jumper 198 isconnected for energizing the No. 1A on indication bus. Relay PLB remainsdown at this time because the No. 1B"on and I98 being connected as shownin Fig. 4.

indication bus 295 is deenergized.

With relay PLA up and relay PLLB down, the A line is deenergized and thereturn circuit for. line S is by way of line B alone, which results indropping relays MA and MAP and holding relays MB and MBP in theiroperated positions. As indicated in the third part of the first onperiod, this is the point in the cycle when the No. 1 on indication isconditioned and in the present example the B line conductor is energizedand the A line conductor is deenergized. With relay MAP down, (B) isconnected to conductor 82 and with relay MBP up, (3+) is connected toconductor 83 for later executing the first on indication.

The picking up of relay VP during the second part of the first on periodopens the circuit of relay E, as has already been described and after atime interval measured off by the slow acting characteristics of relayE, it releases its armature and closes the executing circuits for theNo. l indications which have been conditioned as described.

It will be recalled that relay MX is down, re-

sulting in (13-) being connected to conductor 84, so that this circuitfrom (B') is extended through back contact 85 of relay E, conductor l6(Fig. 3),front contact 8% of relay VP, back contact 37! of relay 3V,front contact 88 of relay IV, No. 1 off indication bus St and winding ofrelay lPT, to (CN). This results in actuating relay iPT to its left handposition as shown.

Recalling that relay MAP is down, a circuit for executing the No. 1A onindication is now com-, pleted, extending from (B-) back contact 90 ofrelay MAP, conductor 82, back contact ill of relay E, conductor Q36,front contact 92 of relay VP,

back contact 93 of relay 3V, front contact lli l of relay lV, No. 1A onindication bus i (35 and winding of relay EPT, to (CN). This results inactuating the contacts of relay ZPT to the left hand position as shownin Fig. 3.

Recalling that relay MBP is up, a circuit for executing the No. IE onindication is now, completed, extending from (B+) front contact fit ofrelay MBP, conductor 83, back contact 95 of relay E, conductor 13!,front contact 96 of relay VP, back contact 91 of relay 3V, front contact98 of relay W, No. 13 on indication bus W9 and winding of relay 3PT, to(ON). in this circuit is in such a direction that relay 3PT will bepositioned to the right as shown.

The system is next advanced into the second off period and as indicatedin the operation chart and as will be evident from an examination of thecircuits above traced, the No. 1 execution circuits remain effectiveduring the first part of the second off period. These execution circuitsare broken at contacts 85, 9! and 95 of .relay E when it is picked up tomark the beginning of the second part of the second off period.

Relay 2V is picked up in the first partof the second off period, closinga circuit for operat ing relay ST of Fig. 3, extending from front Hcontact l2!) of relay 2V, contact 112! of relay IPT in its left handposition, contact E22 of relay ZPT in its left hand position, contactl23 of relay SPT in its right hand position and winding of relay s'r, to

The above explanation sets forth in detail the manner in which thestation shown in Fig. 4, having code combination registers itself in thecontrol office by selecting and operating relay ST of Fig. 3. The codecombination of this station is determined by code jumpers 955 Theselection of one of two combinations during the off period is obtainedby selectively connecting code jumper 1% toindication buses 26%) and 2!as explained. With jumper I96 connected as shown, relay PLA is pickedup, opening line conductor A so that the return circuit is by way ofline conductor B, for picking up relays MB and MBP in the oilice. k MAPdown, relay MX remains down to execute a code as explained. Thealternate connection of jumper I96 to indication bus 28! would result inpicking up relay PLB thus establishing the return circuit by way of theA line conductor so that relay MAP would be up and relay MBP down, whichwould complete a circuit for picking up relay MX. With relay NX up, thecode combination executed is This is the choice of two code combinationsfor the off period.

With jumper 98 connected as shown in Fig. 4, relay PLA is picked up,which opens the A line conductor and establishes the return circuit byway of the B line conductor, so that relay MBP in the control ofiicepicks up and relay MAP stays The current flow With relay MBP up andrelay W60 down. As has been explained, relay MAP down results inpositioning relay ZP'I to the left and relay MBP up establishes acircuit for positioning relay 3PT to the right.

If jumper I98 were connected to indication bus .205, then relay PLBwould be picked up and relay PLA would remain down, which would open theB line conductor and establish the return circuit by way of the A lineconductor. This would pick up relays MA andMAP and leave relays MB andMBP down. With relay MAP up the No. 1A on indication bus of Fig. 3 wouldbe energized for positioning relay ZPT to the right. With relay MBPdown, the No. IE on indication bus would be energized for positioningrelay 3PT to the left.

If jumper I98 is not connected to either bus 204 or 205, then bothrelays PLA and PLB would be down and the return circuit would be by wayof both the A and B line conductors and relays MAP and MBP would both bepicked up. This would result in a potential being applied to both theNo. 1A on and the No. IE on indication buses for positioning relays ZPTand 3PT to the right. This is the method of obtaining a choice of threecombinations during the on period.

It will be understood that there is no combination for positioningrelays 2PT and 3PT both to the left during an on period, because thiswould require both the MA and MB relays being down which is not possibleduring an on period, because one or the other or both the A and B lineconductors must be energized for the return circuit for line S.

The conductor indicated phantom is not used for connection to 'a relaysimilar to ST, because when controls alone are being transmitted, the-off and on combinations provided by the A and B line conductorsinherently result in positioning relay lPT to the left, relay ZPT to theright and relay 3PT to the right. This is due to the fact that both theA and B line conductors are energized in multiple during all of the.conditioning periods, which results in relay MX being down to energizethe No. 1 off indication bus relay MAP being up to energize the No. 1Aon" indication bus and relay MBP being up to energize the No. IE onindication bus Transmission 07 indications-Relays 2V and 2V are pickedup during the first part of the second off period. The No. 2 offindication is conditioned, after the picking up of these two steppingrelays, during the second part of the second off period and the firstpart of the second on period. With relay 2V up and relay VP up at thefield station, a circuit is closed for picking up relay PLB whichextends from back contact I of relay FP front contact I56 of relay SAoff indication bus I91, front contact 2I3 of relay T No. 2B offindication bus 203, front contact 2M of relay2V back contact 2L5 ofrelay 3V front contact 2H3 of relay VP winding of relay PLB and frontcontact I99 of relay L0 to Relay PLA is not picked up during the secondoff period because the No. 2A off indication bus 202 is deenergized.

When relay E of Fig, 2 is picked up, after the picking up of relay 2V,in a manner which has been previously described, relay M'BP is droppedbecause relay E opens its stick circuit at back contact 11. Relay MAP isalready down and the system therefore goes through the second busIH'I atits back contact PLA and PLB down, the pick-up circuit of part of thesecond off period with relays MAP, MBP and MX down. When relay EP dropsand closes the line to advance the system into the first part of thesecond on period, the line S is energized and the return circuit is byway of the A line, because relay PLA is down closing the A line at itsback contact I59 and relay PLB is up opening the B line at its backcontact I53.

Relays F, FP, MA and MAP of Fig. 2 now pick up and. with relay MAP upand relay MBP down, a circuit is closed for picking up relay MX, whichextends from back contact I9 of relay 3V, front contact 20 of relay 2V,front contact 34 of relay VP, back contact 99 of relay EP, back contactI00 of relay MBP, front contact 8| of relay MAP and lower winding ofrelay MX, to Relay MX closes a stick circuit for itself extending fromfront contact IBI of relay FP, front contact B2 of relay MK and upperwinding of relay MX, to Relay MAP is up, relay MBP is down and relay MXis up at this time.

The system is now advanced into the second part of the second on periodby the picking up of relay FP at the field station. The circuit abovetraced, which picked up relay PLB is now interrupted at back contact I55of relay FP so that relay PLB is dropped. This results in energizingboth the A and B line conductors with potential and as a result, relaysMB-and MBP are picked up. With relay MAP up and relay MBP up, thepick-up circuit of relay MX is broken but relay MX remains stuck up topotential at front contact I [II of relay FP.

With the MAP, MBP and PP relays all picked up, the stick circuit ofrelay VP is interrupted at back contacts 60, 59 and 52 of theserespective relays. Relay PLB is dropped, when relay FP disconnectspotential from 01? indication I55. With relays relay VPC is againestablished and this relay is actuated, opens its back contact I13 andinterrupts the stick circuit of relay VP Relay VP drops and establishesthe conditioning circuit for the second on indication. This results inpicking up relay PLA over a circuit extending from front contact 2F ofrelay WP contact 2I8 of relay WP in its right hand position, No. 2A onindication bus 2I9, front contact 201 of relay 2V back contact 268 ofrelay 3V back contact 209 of relay VP upper winding of .relay PLA andfront contact I99 of relay L0 to Relay PLB remains down because the No.2B on indication bus 220 is open at contact 2I8 of relay WP Relay VPC isnow dropped because its circuit is open at contact I90 of relay PLA Thepicking up of relay PLA opens the A line conductor return circuit sothat relays MA and MAP in the control office are dropped. Relay MAP isnow down, relay MBP is up and relay MX is stuck up. The release of relayVP during the second part of the second on period opens the circuit ofrelay E and this latter relay is dropped, after a short time interval.The exeouting circuits are now closed for the No. 2 indications.

Since relay MX is up, a circuit is extended from (3+) front contact I03of relay MX, conductor 84, back contact 85 of relay E, conductor 16,(Fig. 3) back contact 36 of relay VP, front contact I06 of relay 2V, No.2 off indication bus I01, front contact I08 of relay ST and winding ofrelay 1R to (ON). This results in actuating relay IE to the right asshown in Fig. 3.

Since relay MAP is down, the circuit for executing the No. 2A onindication is now complete, extending from (B), back contact 95 of relayMAP, conductor 82, back contact-9i of relay E, conductor I38, backcontact 92 of relay VP, front contact III! of relay 2V, No. 2A onindication bus 'I I I, front contact I I2 of relay ST and winding ofrelay 1R to (CN). This results in actuating the contacts of relay IE tothe left hand position as shown in Fig. 3.

With relay MBP up, the circuit for executing the No. 2B on indication isnow complete, which extends from (13+), front contact 94 of relay MBP,conductor 83, back contact 95 of relay E, conductor I3I back contact 96of relay VP, front contact I it of relay 2V, No. 2B on bus I4, frontcontact I if: of relay ST and winding of relay 1R to (CN). The currentflow in this circuit is in such a direction that relay IE is positionedto the right as shown. I

It will be noted that the stick circuit for relay MBP is effective whenrelay E releases and closes its back contact I7, so that relay MBP willnot be released during the first part of the next off period, with thecircuit through its lower Winding incomplete. The system is nextadvanced into the thir off period and as will be evident from anexamination of the circuits above traced, the No. 2 execution circuitsremain effective during the first part of the third off period. Theseexecution circuits are broken at contacts 85, 9| and 95 of relay E whenit is picked up to mark the beginning of the second part of the thirdoff period. Relays 3V and 3V are picked up during the first part of thethird off period and the No. 3 off indication is conditioned, after thepicking up of these stepping relays, during the second part of the thirdoff period and the first part of the third on period. With relay 3V upand relay VP down at the field station, a circuit is closed for pickingup relay PLA which extends from back contact I55 of relay FP frontcontact I56 of relay SA- off indication bus IS'l, back contact 224of'relay M N0. 3A off indication bus 225, front contact 208 of relay 3Vback contact 209 of relay VP upper Winding of relay PLA and frontcontact I98 of relay L to Relay PLB is not picked up during this offperiod because the No. 313 off indication bus ZZS'is open at frontcontact 224 of relay M When relay E of Fig. 2 is picked up after thepicking up of relay 3V, in a manner which has been previously described,relay MBP is dropped because relay E opens its stick circuit at backcontact TI. Relay MAP is already down and the system therefore goesthrough the second part of the third off period with relays MAP, MBP andMX down. When relay EP drops and closes the line to advance the systeminto the first part of the third on period, the line S is energized andthe return circuit is by way of the B line because relay PLB is downclosing the B line at its back contact I53. Relays F, FP, MB and MBP nowpick up and since relay MAP is down and relay MBP is up, relay MXremains down.

The system is now advanced into the second part of the third on periodwith relays MAP down, MBP up and MX down. When relay FP at the fieldstation picks up to advance the system into the second part of the thirdon period, it interrupts the circuit of relay PLA at contact I55 so thatrelay PLA drops and energizes the A line.

This results in picking up relays MA and MAP so that relays MAP and MBPare both up and relay MX is down at this time.

With relays FP, MAP and MBP all up, the pickup circuit of relay VP iscompleted, extending from front contact 32 of relay SAP, front contact52 of relay FP, front contact 53 of relay MBP, front contact 54 of relayMAP, front contact 55 of relay 3V and winding of relay VP, to At thefield station, a circuit is completed for picking up relay VIPC whenrelay PLA drops and with relay VPC up, the previously described circuitis completed for picking up relay VP except that it now extends throughfront contact 5 81 of relay 3V instead of contact 223 of relay IV Withrelay VP up, the No. 3 on conditioning circuits are established,resulting in dropping both relays PLA and PLB becausethe No. 3A on bus221 and the No. 313 on bus 228 are both shown incomplete in Fig. a. Thisresults in the MA, MAP, MB and MBP relays picking up in the controlofiice and when relay E is released during the fourth part of the thirdon period, the No. 3 indication circuits are executed.

With relay MX down, the No. 3 off indication is executed by means of acircuit extending from (B), back contact I93 of relay MX, conductor a l,back contact 85 of relay E, conductor I6, front contact 86 of relay VP,front contact 81 of relay 3V, No. 3 off indication bus I I6, frontcontact ll! of relay ST and winding of relay 1R to (CN). This results inactuating relay IR to its left hand position as shown in Fig. 3. Ifrelay IE is actuated to the right, lamp M is lighted by way of conductorI21 as an indication that relay M of Fig. 4 is up.

The circuits of the No. 3 on indication buses of Fig. 4 are notcompleted, since it is believed that the examples specifically describedabove are sufficient to indicate how the selection of five indicationchoices is obtained during each step. Likewise, the No. 3 on buses I I8and I I9 of Fig. 3 are not completed, since they may be connected, in anobvious manner, to other relays similar to the IR relays indicated IWith the indication storing relays 1R IE and IE positioned as shown, thecircuits to the indication lamps are selectively conditioned. Sincerelay 1R has its contacts actuated to the right, the circuit to lamp OSis not completed, as an indication that the detector track section isunoccupied as repeated by relay T of Fig. 4 being up. Relays IE and IEcomplete a circuit for lighting lamp NI which extends from contact I24of relay 1B in its right hand position and contact I25 of relay 1R inits left hand position to lamp NI. Lighting lamp NI is an indicationthat the switch TS of Figx is in its normal locked position as repeatedby relay WP The alternate connection of the contacts of relay WP toindication bus 220 would result in opening the B line conductor bypicking up relay PLB ,,so that the return circuit would be by way of theA line conductor alone. This would result in relay MAP being up andrelay MBP being down, so that the No. 2A on indication bus III of Fig. 3would be energizedf-k), to position relay IR to the right and the No.213 on indication bus II -i would be energized to position relay IE tothe left. Likewise, the No. 2 off selection is made by positioning relayMX, in the manner above described, for selectively actuating relay 1R ofFig. 3. Relay 1B

